174 THE ESTIMATION OF PROTEINS. 



ising the milk, using phenol- phthalein as indicator, previous to 

 the addition of the copper sulphate solution ; the quantity of 

 the latter may also be reduced to 2-5 c.c. 



This method gives good results with all milk products, except 

 whey ; this is due to the fact that the copper salts of proteoses 

 are not insoluble in water. There is a slight tendency for the 

 results to be high, owing to copper hydroxide, which is always 

 co -precipitated, not being entirely dehydrated at 130 ; there is 

 also a tendency to be low, because the phosphorus of the casein 

 is converted into phosphoric acid on ignition, which swells the 

 amount of ash. These two errors usually compensate each other 

 to a greater or less extent. 



The washing with alcohol and ether may be omitted, and the 

 precipitate weighed as proteins and fat, the fat, estimated by 

 other methods, being subtracted from the weight. 



Bordas and Toutplain estimate proteins in milk by treating 

 10 c.c. with 20 c.c. of acetone, shaking the mixture to effect 

 complete precipitation, and separating the precipitate in a 

 centrifuge ; the insoluble proteins are collected, washed with 

 dilute and finally with pure acetone, dried, weighed, ignited, 

 and the amount of ash deducted. 



Trillat and Sauton base a method on the fact that formalde- 

 hyde renders the proteins of milk insoluble. Five c.c. of milk 

 diluted with 25 c.c. of water are boiled for five minutes, then 

 treated with 5 c.c. cf 40 per cent, formaldehyde solution, boiled 

 for two or three minutes longer, and allowed to stand for five 

 minutes. The solution is shaken with 5 c.c. of a 1 per cent, 

 solution of acetic acid, and the precipitate collected on a tared 

 filter or Gooch crucible, washed with water, and subsequently 

 extracted with actone to remove the fat. Finally, the precipi- 

 tate is dried at 75 to 80 C., and weighed. 



They have proved experimentally that the protein is com- 

 pletely separated, and that the weight is not increased appre- 

 ciably by the condensation of the formaldehyde. 



Estimation of Casein and Albumin. 



Hoppe-Seyler's Method consists in diluting 10 grammes of 

 milk with about 100 c.c. of water and precipitating the casein 

 by the addition of dilute acetic acid ; carbon dioxide is passed 

 into the solution in order to complete the precipitation. The 

 precipitate is allowed to settle, and the liquid decanted through 

 a tared filter and treated in exactly the same manner as the 

 copper precipitate in Ritthausen's method. The casein, after 

 drying, is ignited, and the weight of the ash, less the weight of 

 the ash of the filter, subtracted from the total weight. 



